Conventional edge-emitting laser diodes are well known. In these diodes, laser radiation is emitted in a plane that is a continuation of the plane of the p-n junction that forms the diode. Different types of these diodes are widely used to provide laser radiation in the infrared and visible regions. While these diodes have enjoyed considerable commercial success, they are relatively large and, as a result, are difficult to integrate with other devices.
Recently, a new class of semiconductor lasers known as a vertical cavity surface emitting laser has been developed. Unlike the edge-emitting laser, these vertical cavity lasers emit laser radiation in the direction perpendicular to the plane of the p-n junction formed in the laser diode. Considerable information concerning the structure and formation of such laser diodes is set forth, for example, in U.S. Pat. No. 4,949,350; in J. Jewell et al., "Microlasers, " Scientific American. Vol. 265, No. 5, pp. 86-94 November 1991); in J. Jewell et al., "Vertical-Cavity Surface-Emitting Lasers: Design, Growth, Fabrication, Characterization, " IEEE Journal of Quantum Electronics, Vol. 27, No. 6, pp. 1332-1346 (June 1991); in G. R. Olbright et al., "Cascadable Laser Logic Devices: Discrete Integration of Phototransistors with Surface-Emitting Laser Diodes," Electronics Letters, Vol. 27, No. 3, pp. 216-217 (Jan. 31, 1991); in J. Jewell et al., "Low-threshold Electrically-Pumped Vertical-Cavity Surface Emitting Lasers," Electronics, Lett., Vol. 25, p. 1123 (1989); and in J. Jewell et al., "Vertical Cavity Lasers for Optical Interconnects," SPIE Vol. 1389 International Conference on Advances in Interconnection and Packaging, pp. 401- 407 (1990), all of which are incorporated herein by reference.
As set forth in certain of the above-referenced publications, vertical cavity lasers have numerous advantages over edge-emitting lasers, some of the most important of which are that they can be fabricated in extremely small sizes (e.g., on the order of one micrometer in diameter) and can be integrated with other devices such as transistors.